Work vehicles such as wheel loaders known in the related art typically include a rotatable arm and a rotatable bucket mounted at the front end of the arm. The rotational motion of the arm and the bucket in such a work vehicle in the related art may be induced as they are driven via a tandem hydraulic circuit that gives priority to the rotating operation of the bucket over the arm (see patent literature 1). However, there is an issue that remains to be addressed in that arm drive is interrupted while the bucket is engaged in rotating operation, and thus the arm can no longer move smoothly. Accordingly, a parallel hydraulic circuit system that drives the arm and the bucket to engage them in rotating operation concurrently has been proposed for work vehicles (see patent literature 2).